This invention relates to an apparatus and method for operation of an ore processing furnace for improved processing of iron oxide reduction. More particularly, this invention relates to the method of operation of a furnace for production of high purity iron and an improved furnace apparatus for iron reduction.
In 1987, Midrex received U.S. Pat. No. 4,701,214, that taught reduction in a rotary hearth furnace and a method of operation which required less energy and a smaller smelting furnace by introducing reductant gases and fuel into the rotary hearth furnace.
All major steelmaking processes require the input of iron bearing materials as process feedstocks. For a steelmaking method utilizing a basic oxygen furnace, the iron bearing materials are usually blast furnace hot metal and steel scrap. A broadly used iron source is a product known as Direct Reduced Iron (xe2x80x9cDRIxe2x80x9d) which is produced by the solid state reduction of iron ore without the formation of liquid iron. DRI and/or steal scrap are also used for steelmaking utilizing the electric arc furnace.
Improvements are sought within the industry for furnace modifications and improved methods of operation that provide for efficient production of high purity iron with low carbon ( less than 5%) material in which iron oxides are efficiently reduced into purified iron on a hearth surface while slag components are separated from purified iron at increased temperatures.
In 1998, Midrex International received U.S. Pat. No. 5,730,775, that teaches an improved method known by the trade name or trademark of FASTMET(trademark), and apparatus for producing direct reduced iron from dry iron oxide and carbon compacts that are layered no more than two layers deep onto a rotary hearth, and are metallized by heating the compacts to temperatures of approximately 1316xc2x0 to 1427xc2x0 C., for a short time period. For a general understanding of the recent art, U.S. Pat. No. 5,730,775 is herein incorporated by reference.
In the direct reduction of iron oxide in furnaces, this invention improves the utilization of a rotary hearth furnace using a method for producing high purity iron product from iron oxide feed material containing carbon compounds, including the steps of providing a rotary hearth furnace having a hearth layer which consists of a refractory layer or a vitreous hearth layer formed by placing iron oxide, carbon, and silica compounds on the sub-hearth layer; heating the iron oxide, carbon, and silica compounds forming a vitreous hearth layer; placing coating materials on the hearth surface to form a coated hearth layer; feeding iron oxide material into the furnace and onto the coated hearth layer; heating the iron oxide material on the coated hearth layer; reducing the iron oxide materials on the coated hearth layer; forming liquid iron and carbon globules on the coated hearth layer, with separated slag materials; cooling the iron and carbon globules with a cooling surface, creating a solid button of iron and carbon product; and discharging iron and carbon product and slag material from the furnace. An improved apparatus includes a rotary hearth furnace having a cooling plate that is placed in close proximity with the hearth layer or refractory surface, the cooling plate cools the iron globules to form solid high purity iron and low carbon buttons that are removed from the vitreous hearth layer. The improvements due to the present apparatus and method of operation are providing high purity iron and low carbon buttons which are separated from the slag particulates, discharging the buttons from the furnace without significant loss of high purity iron in the hearth furnace, and generating iron buttons with iron content of approximately 95% or greater, and carbon content of approximately 5% or less in the discharged buttons of iron material.
The principal object of the present invention is to provide a method of achieving efficient production of high purity iron having concentrations of carbon of 1% to 5% therein at elevated temperatures in a rotary hearth furnace with separation of slag components from the purified iron on the hearth surface at high temperatures.
Another object of the invention is to provide a method of achieving efficient reduction of iron oxide at elevated temperatures in a processing and reducing furnace.
An additional object of the invention is to provide an improved furnace apparatus for providing high purity iron and cooling the high purity iron on the hearth layer surface to facilitate separation of slag components within the furnace.
The objects of the invention are met by a method for producing direct reduced purified iron at elevated temperatures within a furnace, including the step of providing a rotary hearth furnace having a sub-hearth layer, and introducing conditioning materials of iron oxide, carbon, and silica compounds with heating of conditioning materials to form a vitreous layer onto which agglomerates of iron oxide containing carbon are placed. The step of heating the conditioning materials proceeds the step of reducing by heating the agglomerated iron oxide and carbon, at a specified temperature, and reducing the iron oxide. The molten globules of purified iron are separated from slag components on the hearth layer surface within the furnace. A cooling step follows the separating step, where globules of purified iron are cooled within the furnace by placing a cooling apparatus in close proximity to the hearth layer, with the resulting step of solidification of purified iron within the furnace, and the remaining step of discharging the purified iron from the furnace free of solidified slag, which may be discharged separately from the furnace.
The objects of the invention are also met by an apparatus for producing direct reduced iron at elevated temperatures within a rotary hearth furnace having a non-reactive hearth surface made by the placement of coating materials and agglomerates of iron oxide and carbon onto the surface of the hearth layer. The hearth layer may include a vitreous layer of iron oxide and silica compounds formed before the agglomerates of iron oxide and carbon are placed onto the vitreous or the refractory layer. The coating materials and agglomerates of iron oxide and carbon are heated to a specified temperature. The iron oxide is reduced followed by separation into globules of purified iron from the slag components and coating materials on the hearth layer. The purified iron is solidified by passage of the liquid iron globules in close proximity to a means for cooling above the hearth layer consisting of exposure to cooled apparatus placed close to the hearth layer or refractory surface. After passage past the means for cooling on the hearth layer or refractory surface, the purified and solidified iron and low carbon buttons are removed from the hearth layer for collection outside of the rotary hearth furnace separate from slag particulates formed within the furnace.